A common requirement in current advanced semiconductor processing is for wafer rinse and clean processes. Wafer rinse or clean is performed at various stages in the processing and may remove particles or residues left by a prior process. For example, patterned films such as dielectric layers may be cleaned to remove particles. While in past generations of semiconductor tools, a batch rinse station might be used which applied de-ionized water (“DIW”) or other cleaners to a number of wafers arranged in a boat or carrier by spray or immersion techniques, more recently single wafer cleaning stations have been used. As wafer sizes increase to the current 300 millimeter (“12 inch”) and the coming 450 millimeter (“18 inch”) sizes, the use of single wafer tools is becoming even more prevalent.
In the current single wafer cleaning tools, a wafer may be mounted on a platen or chuck with its active face oriented upwards, for example, and a spray nozzle may apply deionized water (“DIW”) or other cleaning solutions or solvents under pressure. The spray nozzle may travel across the wafer. For example if the wafer is rotating about a central axis, the nozzle may travel rectilinearly across half or all of the wafer to enable the nozzle to spray the entire wafer surface. The speed the nozzle travels relative to the wafer surface is the nozzle “scan speed”. However, the use of pressure provided, for example, by aerosol and DIW sprayed on a wafer surface by a moving spray nozzle can damage wafers. In some systems, the nozzle pressure can be controlled and raised and lowered. However, even when low pressure is used, “outlier” droplets from the spray nozzle can still impact the wafer surface at greater velocity than desired, which may cause pattern damage. These fast moving outlier droplets can transfer their kinetic energy to a loose particle, which as it travels away from the wafer surface, may collide with a portion of the pattern and damage the pattern. A lower nozzle spray pressure may be used to avoid the damage, but this lowered pressure results in lowered particle removal efficiency. That is, a tradeoff exists in conventional wafer cleaning tools between the velocity or nozzle pressure of the spray DIW, and the particle removal efficiency (“PRE”) obtained.
A continuing need thus exists for methods and apparatus for cleaning wafers with high particle removal efficiency and without the disadvantages currently experienced using known methods.
The drawings, schematics and diagrams are illustrative and not intended to be limiting, but are examples of embodiments of the invention, are simplified for explanatory purposes, and are not drawn to scale.